The present invention is directed to weighing apparatus calibration and more specifically to a method for managing the calibration of weighing apparatus.
Installations such as scales, weigh platforms, vessels (such as silos, tanks and hoppers) or other weighing apparatus are used in many processes for information and process control purposes. These installations usually have a working configuration of at least one load cell. The load is usually transmitted to the working load cell through a support bracket or other special bearing surface, adapted to carry its weight and the weight of any contents. Typically, three or four working load cells, with corresponding supports, are used in any one installation, so the aggregate load is the sum of all the separately measured loads. Some weighing apparatus may use a mechanical arm system to transfer their weight to a single load cell. Additional details of the functions of load cells can be found in U.S. Pat. No. 6,576,849, which is hereby incorporated by reference.
Such installations may need to be calibrated from time to time. This may be because of drift or creep in the electrical or mechanical properties of the load cells, in the tare of the weigh platform or vessel, or after a repair. It may not be practicable to remove the load cell or cells from the installation for re-calibration because of the substantial impact this will have on the availability of the installation. In an industrial process, it may mean production downtime. Instead, different methods have been adopted. One such method includes placing a known test mass equaling the total weighing capacity of the installation on the weighing apparatus. The system compares the known test mass with the total weight indicated by the working load cells. The technician or terminal then calibrates the system to that known test mass. The indicated total weight is conventionally the single integrated or summated output of all load cells combined. Conventional weighing calibration takes the whole system into consideration, including all load cells, sources and measures of applied excitation voltage to the load cells, and meters for interpreting the corresponding load cell output signals. A necessary consequence is that, if any part of this system fails or is adjusted or replaced; the whole system must be recalibrated.
When sufficient test masses are not available to perform the calibration function, a process known as step or substitution calibration may be used. In this technique, a technician places a known test mass, which is less than the total weighing capacity of the installation, on the weighing apparatus and calibrates the weighing apparatus to that load point. The technician removes the test mass and adds a substitute material to bring the indicated weight substantially close to the test mass' weight. The technician places the test mass back on the weighing apparatus. Next, the technician calculates the total weight of the test mass and the material and inputs the amount into the terminal. The technician re-calibrates to the new total load point. The process is repeated until the total load calibrated is close to the total weighing capacity of the weighing apparatus. This process is cumbersome and requires manual data entry at each of the various steps during the calibration. Additionally, the technician performing the calibration must calculate the indicated weight and the known test mass either with the aid of a calculator or in his or her head creating the possibility of errors.
Exemplary embodiments of the present invention may automate and manage the calibration process. A calibration management system monitors the weighing apparatus to determine if a limit is exceeded. If the limit is exceeded, the system instructs a technician, through a series of prompts, to run a calibration test. If the test is performed successfully, the calibration manager is reset. If the test is not successful then an event may occur. The event may be: displaying a message on the terminal's screen; sending a message by email, instant message or fax to a predetermined location, deactivating the weighing apparatus and/or any combination thereof. Additionally, an action may be performed, such as a repair or re-calibration of the system. During calibration of the system, increments of weight are added to the weighing apparatus based on prompts initiated by the terminal and followed by the technician. This is opposite of the known approach. In exemplary embodiments of the present invention, the terminal instructs the technician and not vice versa.